What is Particulate Matter?

Most people have no idea what particulate matter (PM) is, let alone, that there is such a thing as particle pollution. We might think that pollution is just "something that floats in the sky way above our head" or that it is far away because it can only been seen in the distance. This thinking is wrong, in fact, pollution surrounds us no matter where we are or what we’re doing. Even on a clear day it’s everywhere, in the atmosphere, at ground level, and yes, even in our homes. Particulate matter floats through the air and with every breath we take we breathe it in, and most of it isn't visible to the naked eye. Although so small as to be invisible, PM is the air pollution that most commonly affects people’s health.

Particle pollution is produced in a great number of ways that can be classified into either mechanical or chemical processes. The mechanical process of particle pollution involves the breaking down of bigger matter into smaller particles without the material changing, only becoming smaller. Agriculture, coal and oil combustions, dust storms and construction are some activities that produce many of the larger or coarse particles. The chemical process of particle formation can be from sources that burn fuel and emit gases. Here, the pollutant vaporizes and then condenses to become a particle of the same chemical compound. The small particles can further react or combine with other compounds in the atmosphere. A major source for particles formed this way are the burning of fossil fuels in industry, transportation, agriculture, etc.

Particles come in many, many shapes and sizes, and can be solid particles or liquid droplets. The size of particles is directly linked to their potential for causing heath problems. Traditionally, the environmental sciences have divided particles into two main groups and these two groups are different in many ways. PM10 is particles between 2.5 and 10 microns (micrometers) in diameter (a human hair is about 60 micron in diameter). PM2.5 is particles smaller than 2.5 microns. The PM10 and PM2.5 measurements you might have seen reported, by the EPA for example, refer to the total weight of the particle found. This is a holdover from when the available technology had difficulty detecting individual particles. More modern monitoring equipment, such as that used in clean room monitoring, count and size individual particles. The Dylos DC1100 is this more modern type of device and counts individual particles in two size ranges which will roughly correlate to PM2.5 and PM10.

There is more than size that is different in these types of particles. Each type of particle has different material compositions and can come from different places. The smaller the particle the longer it can remain suspended in the air before settling. PM2.5 can stay in the air from hours to weeks and travel very long distances because it is smaller and lighter. PM10 can stay in the air for minutes to hours and can travel shorter distances from hundreds of yards to many mile because it is larger and heavier.

When you inhale, you breathe in air along with any particles that are in the air. This breath of air, along with the particles, travel into your respiratory system, and along the way the particles can stick to the sides of the airway or travel much deeper into the lungs. Your lungs produce mucous to trap particles and there are also tiny hairs (called cilia) that move the mucous and particles out of the lungs. PM2.5 can get down into the deepest (alveolar) portions of the lungs when gas exchange occurs between the air and your blood stream. These are the most dangerous particles because the alveolar portion of the lungs has no efficient means of removing them and if the particles are water soluble, they can pass into the blood stream within minutes. If they are not water soluble, they remain in the alveolar portion of the lungs for a long time.

However, when the small particles go deeply into the lungs and become trapped this can result in lung disease, emphysema and/or lung cancer in some cases. Exercise and physical activity cause people to breather faster and more deeply and to take more particles into their lungs. The United States Environmental Protection Agency reported “studies suggested small particles can leave the lung and travel through the blood to other organs, including the heart”.

The main effects associated with exposure to particulate matter may include: premature mortality, aggravation of respiratory and cardiovascular disease (indicated by increased hospital admissions and emergency room visits, school absences, loss of work days, and restricted activity days) aggravated asthma, acute respiratory symptoms, chronic bronchitis, decreased lung function and increased myocardial infarction. Epidemiologic studies suggest that exposure to particulate matter may result in tens of thousands of excess deaths per year, and many more cases of illness among the US population.

People with heart or lung diseases such as coronary artery disease, congestive heart failure, and asthma or chronic obstructive pulmonary disease (COPD) are at an increased risk, because particles aggravate these diseases. People with diabetes also may be at an increased risk, possibly because they are more likely to have underlying cardiovascular disease, and older people may be at greater risk due to undiagnosed heart or lung disease or diabetes. Infants and children are also at risk for several reasons, first their lungs are still developing and they have an increased level of activity and play. This is when they would be more likely to have asthma or acute respiratory disease, which is aggravated when particle levels are at their highest. It has also been suggested that high exposure to particle levels may attribute to low birth weights in infants, pre-term deliveries and possible fetal and infant deaths.